1. Field of the Invention
This invention relates generically to joinder of plastic conduit to other conduit. More particularly, this invention relates to method and apparatus for making a combination thermoplastic conduit having integrally formed washer for effecting joinder to other pipe or the like.
2. Description of the Prior Art
The prior art has seen the introduction of a wide variety of types of conduits and methods of joining of the conduits, whether they were of the same or of dissimilar materials. A large improvement in plumbing technology was made when copper pipe began to be employed. The price of copper has risen so dramatically, however, that it is economically infeasible in many applications. Its successor was plastic pipe, or tubing, which had some advantages even over the copper pipe and was more economical. One recent innovation that is seeing increasingly widespread use is the use of plastic conduits, such as polybutylene pipe, or tubing, in low pressure applications.
In my co-pending application "Joinder of Plastic Pipe to Other Pipe", Ser. No. 728,232, filed Sept. 30, 1976, I described the problems that have plagued the industry and delineated therein an improvement and the descriptive matter that application is incorporated herein by reference. Specifically, one of the problems was the joinder of the plastic pipe to other types of conduit, such as wrought iron pipe, frequently employed in home construction. One of the advantages of the plastic pipe is that it does not set up galvanic cells as did the copper tubing. The prior art has seen different approaches ranging from the use ferrule fittings to the use of preformed ends to be joined with the plastic pipe, such as described in U.S. Pat. No. 3,831,983, the closest art of which I am aware. In that patent, the preformed end is fused into the end of the plastic conduit and thereafter forced interiorly of and in swaging relationship with carefully preformed shoulders to form a seal. While that method had advantages over the art theretofore, it was relatively expensive since the fittings had to be so carefully prepared. Also, application in the field required stocking a relatively complete range of sizes that had been carefully prepared at the factory. In my own co-pending application, I described the forming of an integral washer onto the plastic tubing, as by inserting the end onto a flat plate or within a mold and allowing the plastic, such as polybutylene, to melt and roll back in upon and cohere to itself to form the washer. That innovation has been extremely useful and successful, but the washer did not have enough inherent resiliency to hold a fitting tightened into place with total success in preventing loosening of the fitting; and did not alleviate the problem of breaking adjacent a heating line.
Also the washer did not have adequate resiliency to insure sealing all of the time regardless of the roughness of the fitting against which it was seated. Moreover, the forming of the washer was done in the field by a plumber on an individual basis, so it was time consuming, slow, and expensive.
Thus it can be seen the prior art has not been totally successful in providing an inexpensive method and apparatus for effecting joinder of plastic pipe to other conduit while retaining sealing and tightened fittings and otherwise obviating the disadvantages of the prior art structures.